56 



MANUAL OF ZOOLOGY. 



with vibratile filaments or cilia (fig. 9 c, c). The pores open 

 into these chambers, and from them proceed the incnrrent 

 canals, each being dilated at its commencement into a sac, 

 which is also lined with ciliated sponge-particles. By the 



Fig. 9. Diagrammatic section of SpongiUa (after Huxley), a a. Superficial 

 layer or ' dermal membrane.' 6 6. Inbalent apertures or ' pores.' c r. 

 Ciliated chambers, d. An exhalent aperture or ' osculum.' The arrows 

 indicate the direction of the currents. 



vibratile action of these cilia currents of water are caused to 

 set in by the pores, and as out-going currents proceed from 

 the oscula a constant circulation of fresh water is maintained 

 through the entire sponge. In this way each individual 

 sponge-particle is enabled to obtain nutriment ; the process 

 being at the same time not improbably a rudimentary form of 

 respiration. 



The reproduction of sponges may be effected either 

 asexually or sexually, the following being a brief outline of 

 the phenomena which have been observed in the common 

 fresh- water sponge (Spongilla), in which the process has been 

 most accurately noticed. 



In the first or asexual method of reproduction, which takes 

 place in the winter, the deeper portions of the sponge are 

 found to be filled with small seed-like rounded bodies, 

 termed 'gemmules' or 'spores,' each of which possesses a 

 small aperture or 'hilum' at one point. Each gemmule is 

 composed of an outer coriaceous capsule surrounded by a 

 layer of peculiar asteroid spicula, resembling two toothed 

 wheels united by an axle, and termed ' amphidiscs.' These 

 amphidiscs are imbedded in sarcode, whilst their inner sur- 

 faces rest upon the tesselated capsule already mentioned. 

 The contents of the capsule are mostly sponge-particles which 

 have developed ovules in their interior. When the spring 

 comes, these ' ovi-bearing cells ' are discharged through the 



